tirapazamine and Carcinoma--Small-Cell

To determine the feasibility and a recommended phase II dose of tirapazamine when combined with chemoradiotherapy in limited-stage small cell lung cancer (LSCLC).. Concurrent chemoradiotherapy consisted of two cycles of cisplatin, etoposide, and once-daily radiation to 61 Gy. Tirapazamine (260 mg/m2) was given 1 h before cisplatin with planned dose escalation to 330 mg/m2 in the absence of dose-limiting toxicity, defined as > or =33% esophagitis (grade 3 or above). Consolidation therapy consisted of two cycles of tirapazamine (330 mg/m2), cisplatin, and etoposide. Complete responders received prophylactic cranial irradiation.. Thirty patients were enrolled at the 260 mg/m2 tirapazamine dose. All had performance status of 0-1. By comparison with S9713, a predecessor Southwest Oncology Group study in LSCLC that used the same concurrent chemoradiotherapy without tirapazamine, the present trial showed a higher rate of grade 3-4 esophagitis (34% versus 22%), vomiting (34% versus 23%), and febrile neutropenia (7% versus 2%). The consolidation phase was relatively well tolerated, with grade 4 neutropenia in 44% and febrile neutropenia in 5% of patients. There were two treatment-related deaths: one from neutropenic fever and one from respiratory infection. The overall response rate was 80%, and the median survival was 22 months.. Protocol-defined dose-limiting toxicity was observed at the initial tirapazamine dose, precluding dose escalation. Compared with S9713, the addition of tirapazamine increased the incidence of vomiting, neutropenia, and febrile neutropenia, although the overall toxicity profile remained acceptable. In view of the observed favorable survival, further study of tirapazamine in LSCLC is warranted.

Topics: Adult; Aged; Antineoplastic Combined Chemotherapy Protocols; Carcinoma, Small Cell; Cisplatin; Combined Modality Therapy; Esophagitis; Etoposide; Female; Humans; Lung Neoplasms; Male; Middle Aged; Neutropenia; Radiation-Sensitizing Agents; Radiotherapy Dosage; Tirapazamine; Triazines; Vomiting

Carbonic anhydrase 9 (CA9) is over-expressed in many human solid tumors under conditions of low oxygen concentration and can be associated with a low probability of survival. In this study, stable CA9-expressing cell lines were established using the CA9 gene-defective human C33a cell line and the HeLa cell line to investigate the role of CA9 in response to ionizing radiation and hypoxia-selective cytotoxin, Tirapazamine (TPZ).. Human CA9 cDNA or an empty vector was transfected into the C33a and HeLa cell lines and C33a-vector, C33a-CA9, HeLa-vector, and HeLa-CA9 cell lines were produced accordingly. Sensitivity of the C33a-vector/C33a-CA9 cells to ionizing radiation and TPZ was measured using clonogenic assays. The alkaline comet assay was used to measure single strand DNA breaks caused by TPZ in the C33a-vector, C33a-CA9, HeLa-vector, and HeLa-CA9 cell lines.. Radiation sensitivity, as determined with clonogenic survival assays, of C33a-vector/C33a-CA9 cells did not differ under either normoxic or hypoxic conditions. However, increased clonogenic sensitivity to TPZ was observed in C33a-CA9 cells under the hypoxic condition by 26% (95% CI 14-39%, P = 0.02 in comparison to the C33a-vector cells). The comet assay showed significantly greater DNA damage in the C33a-CA9 cells compared with that of the C33a-vector cells with the same treatment under hypoxic conditions, supporting the results of the clonogenic survival data. Because this difference in the amount of DNA damage was not observed for the hypoxic HeLa-CA9/HeLa-vector cell lines, both of which have induced CA9 expression by hypoxia, the enhanced sensitivity of C33a-CA9 cells to TPZ is considered to be due to the specific condition of CA9 over-expression.. Our results suggest the possibility that CA9 over-expression in tumors might be exploited to increase the treatment effects of TPZ.

Topics: Antigens, Neoplasm; Carbonic Anhydrase IX; Carbonic Anhydrases; Carcinoma, Small Cell; Cell Hypoxia; DNA Damage; DNA, Neoplasm; Dose-Response Relationship, Radiation; Gene Expression; HeLa Cells; Humans; Radiation-Sensitizing Agents; Tirapazamine; Transfection; Triazines; Tumor Cells, Cultured

Tirapazamine (TPZ), a hypoxia-selective cytotoxin, has demonstrated activity in cancer clinical trials. Under hypoxic conditions, TPZ is reduced to a radical that leads to DNA double-strand breaks (DSBs), single-strand breaks, and base damage. A previous finding of an association of the DSBs with protein led us to investigate the involvement of topoisomerase II (topo II) in their formation. Nuclear extracts from human lung cancer cells treated with either the topo II poison etoposide or TPZ under hypoxic conditions had markedly reduced topo II activity as judged by an inability to convert kinetoplast DNA from the catenated to the decatenated form. Because topo II poisons, such as etoposide, cause DNA DSBs, we hypothesized that pretreatment of cells with merbarone or aclarubicin, known catalytic inhibitors of topo II, would abrogate DNA DSBs caused by topo II. Cells pretreated with these catalytic inhibitors abrogated both DNA DSBs and cell kill induced by etoposide or by TPZ. Etoposide- and TPZ-mediated DSBs were also greatly reduced in a small cell lung cancer cell line with low levels of nuclear topo IIalpha. We also showed that topo IIalpha becomes covalently bound to DNA after TPZ treatment under hypoxic conditions, and that the cleavable complexes formed by TPZ are more stable over time than those formed by etoposide. Taken together, these data suggest that TPZ exerts its cytotoxic effect at least in part through poisoning topo II. Because TPZ is activated only under hypoxic conditions, which are characteristic of solid tumors, these data implicate TPZ as a tumor-specific topo II poison.

Topics: Antineoplastic Agents; Carcinoma, Non-Small-Cell Lung; Carcinoma, Small Cell; Cell Hypoxia; DNA Damage; DNA Topoisomerases, Type II; DNA, Neoplasm; Enzyme Inhibitors; Etoposide; HeLa Cells; Humans; Lung Neoplasms; Tirapazamine; Topoisomerase II Inhibitors; Triazines